[Intel-gfx] [PATCH 13/16] drm/i915: don't use the first stolen page on Broadwell

[Ville Syrjälä]

On Wed, Aug 26, 2015 at 09:48:51AM +0200, Daniel Vetter wrote:
> On Wed, Aug 19, 2015 at 02:55:34PM +0300, Ville Syrjälä wrote:
> > On Sat, Aug 15, 2015 at 09:30:18AM +0100, Chris Wilson wrote:
> > > On Fri, Aug 14, 2015 at 06:34:18PM -0300, Paulo Zanoni wrote:
> > > > The spec says we just can't use it.
> > > 
> > > But what about when we inherit a framebuffer at that address?
> > 
> > Indeed. I asked the same question several times during the past attempts
> > at this, and even tried to outline a potential solution at least once [1]
> 
> Paulo's only patching the insert_node_in_range allocator, for fbcon
> takeover we use reserve_node. I think this patch seems to do what you want
> it to do, no need for fancier schemes.

Hmm. Indeed. It's a somewhat surprising place to find such a check, but
it does solve the preallocated vs. normal issue. It does mean we may
end up with some corruption in the fbdev bo but I suppose that's short
lived enough that we can ignore it.

It could use a comment as to why we put the check there instead of
totally removing the first page from the stolen mm. Otherwise someone
might decide to clean it up and break things. Also lacking the w/a name
and some explanation why it's needed. And as I mentioned before, CHV
needs to be included. SKL/BXT only have it listed for early steppings,
so I think we can ignore those.

-- 
Ville Syrjälä
Intel OTC